Fire alarming system

ABSTRACT

A fire alarm system having a plurality of fire detectors connected in parallel to a transmission line, each detector having a band pass filter resonating at a specific individual frequency. A receiver is connected to the transmission line and generates a plurality of frequencies corresponding to the frequencies of the detectors and has means for detecting specific frequencies returned thereto when one or more of the detectors are activated by fire, thus enabling detection and location of a fire.

11113 10 States 0801 11 1 Honda 1 51 Aug. 14, 1973 [54] FIRE ALARMINGSYSTEM 3,588,892 6/1971 Scheidweiler 340/228 X 9 7 1 3 1 1 Inventor:Yukio Honda, Nakano-ku, Tokyo, 3253134 311327 5112;??? 328155532 Japan3,378,829 4/1968 Alafi et a1. 340/227 3,626,316 12/1971 Connell, Jr.340/227 X [73] Assgnee' Company Tokyo 3,484,775 12/1969 Cline 340/224 x3,402,404 9/1968 Burley 340/413 x [22] Filed: Mar. 10, 1971 3,399,3818/1968 Jackson 340/171 PF [21] Appl. N0.: 122,956 FOREIGN PATENTS ORAPPLICATIONS 666,082 7/1963 Canada 340/408 [30] Forelgn Apphcapon PnomyData Primary Examiner-John W. Caldwell Mar. 31, 1970 Japan 45/26844Assistant Examinergscon R Partridge Mar. 31, 1970 Japan.. 45/26843 y gGeoffrey Jr.

[52] US. Cl..... 340/228 R, 340/171 PF, 340/237 S,

340/408 [57] AB'STRACT 51 1111. c1. (3030 25/00 A fire System havmg P fP 9 fire detwors [58] Field of Search 340/227, 228, 191, connecfedParallel to a 9 9 340/179, 181, 408 182, 185, 224, 171 tc r havmg a bandpass filter reson atlng at a spec1fic1n- 184,413,416171,237;31O/81;.343/6 5,6 5 d1v1dua 1 frequency, A rece1ver 1s connected to the SStransmlsslon lme and generates a plurahty of frequencies correspondingto the frequencies of the detectors [56] References Cited and hashmeansfor detecting specifgchfrequencies re- UNITED STATES PATENTS turned tereto when one or more o t e detectors ere actwated by fire, thusenablmg detectlon and locatlon 3,550,090 12 1970 Baker, Jr. et a1.340/408 x of a 3,564,524 2/1971 Walthard et al. 340/228 X 3,445,8435/1969 Pena 3lO/8.l X 4 (Ilaims, 11 Drawing Figures /7 9/04 l8 27 r---3.--- 134 P 1 6 E g l I IV I U L 1 w l I u 1 l 1 :1 5 a 1 f 1 FIREALARMING SYSTEM This invention relates to a fire alarm system and moreparticularly to such a system including novel and improved means indetecting the location of a fire.

In the prior fire alarm systems, a number of fire or smoke detectors aregenerally connected in parallel between a pair of conductors which areconnected to a single receiver including a power supply and an alarmdevice. When any of the detectors is excited, a closed circuit includingthe power supply and alarm device is completed through said detector andan alarm signal is generated from the alarm device. In such a fire alarmsystem, however, the alarm signal is generated whenever at least one ofthe detectors is excited but it cannot indicate which detector has beenexcited. That is, such system can only detect a fire but cannot detectwhere the fire has started. Therefore, the prior fire alarm system hasrequired other means, such as patrols for finding the location of thefire. However, such a procedure is difficult especially when largenumbers of detectors are distributed over a wide area or in a tallbuilding.

In order to overcome this difficulty in some of the prior systems, thedetectors are individually connected to the receiver, but such systemsrequire a bulky bundle of cables and the cost of installation is high.As described in a co-pending U.S. Pat. application, Ser. No. 120,178,filed Mar. 2, l97l, this inventor describes a novel system wherein eachof the detectors includes an oscillator which generates its owncharacteristic frequency when excited and the receiver includes meansfor detecting the frequency and indicating the corresponding detector.Although the system is very effective in comparison to the priorsystems, the detectors are rather bulky and costly.

Therefore, one object of this invention is to provide an improved lowcost fire alarm system which can quickly indicate any detector now beingexcited.

According to this invention, each of the detectors includes a filterwhich can pass only its own characteristic frequency when excited andthe receiver includes means for generating AC signals having at leastthe characteristic frequencies of the detectors and means for detectingthese frequencies and indicating the corresponding detectors. Therefore,the system of this invention can generate an alarm signal and at thesame time indicate the detectors being excited. In addition, thedetectors of this system can be made rather compact and at a low costsince they have few and relatively simple structural components.

Other features and operation of this invention will be more clearlyunderstood from the following description and the accompanying drawings.

In the drawings:

FIG. 1 is a diagram representing partly 'inblock form a general circuitconfiguration of a prior fire alarm system;

FIG. 2 is a diagram representing, partly in block form, a circuitconfiguration of an ionization type smoke detecting system including anembodiment of this invention;

FIG. 3(1) and 3(2) are schematic circuit diagrams explaining operationof the embodiment of FIG. 2;

FIG. 4 is a schematic circuit diagram representing an ionization smokedetector in accordance with another embodiment of this invention;

FIGS. 5(1) and 5(2) are schematic circuit diagrams explaining theoperation of the embodiment of FIG. 7;

FIGS. 6(1) and 6(2) are schematic diagrams representing a soundingdevice to be included in the detector of this invention;

FIG. 7 is a schematic diagram representing a circuit configuration of abimetal type fire detecting system and the construction of the detectorin which this in vention is embodied; and

FIG. 8 is a block diagram representing a further embodiment of firealarm system according to this invention.

Throughout the drawings, like reference numerals are used to denote likestructural components.

Referring first to FIG. 1 representing a prior fire alarm system, anumber of fire detectors 10-1, 10-2, 10-n are connected in parallelbetween a pair of conductors 1 and 2 which are respectively connected tothe both input terminals 7 and 8 of a receiver 11. The receiver 11includes an electromagnetic relay 12, a power supply 13 indicated as abattery and connected in series with the electromagnet of the relay 12between both input terminals 7 and 8. Another power supply 14 isindicated as an AC source and is connected in series with the normallyopencontact of the relay 12 and an indicating lamp 15 and a soundingdevice 16 such as a bell or buzzer which is connected in parallel withthe indicating lamp 15. Although there are many types of detectors 10,most of them can be represented by a single-pole, single-throw normallyopen switch as indicated schematically in the drawing, which is closedwhen the detector is excited.

When any of the detectors of the system is excited, a closed circuitincluding the power supply 13 and the realy 12 is completed to energizethe relay l2 and close its contact and thus the existance of a fire isindicated by the lamp 15, and an alarm is sounded by the sounding device16. As readily understood, in the such system, the receiver can indicatetheexistance of a fire but cannot indicate the site of the fire sincethe relay 12 is energized similarly by any of the detectors beingexcited.

Referring now to FIG. 2 representing an embodiment of this invention, anumber of detectors 10-1, 10-2, are connected in parallel between a pairof conductors 1 and 2 which are respectively connected to inputterminals 7 and 8 of a receiver 11. The receiver 11 also has a thirdterminal 9 connected to a third conductor 3 which is in turn connectedto each of the third output terminals of the respective detectors.

As shown in detail in the first detector 10-1 only, each of thedetectors consists of a fire detecting section 17 and a frequencyfiltering section 18. The fire detecting section 17 of this embodimentconsists of an ionization type smoke detector including, as well-knownin the art, a closed ionization chamber 19 having a pair of electrodes21 and 22 and a radioactive source 23 for ionizing the ambient air andan open ionization chamber 20 having a similar pair of electrodes 24 and25 and a radioactive source 26. The electrodes are connected in seriesbetween terminals 4 and 5 of the detector which in turn are connected tothe conductors l and 2, respectively. The smoke detector also includes afield effect transistor 27 having a gate electrode connected to thejunction between the both ionization chambers 19 and 20 and adrain-source conduction path connected through a load resistor 28between the both terminals 4 and 5, and a silicon controlled. rectifier30 having a conduction path connected also between the terminals 4 and 5and a control electrode connected through a zener diode 29 to the sourceelectrode of the field effect transistor 27. A specific operationvoltage is always applied between the both terminals 4 and 5 by a powersupply 13 included in the receiver 11.

As well-known in the art, when smoke enters the open ionization chamber20, it acts to raise the impedance of the chamber and consequently thevoltage at the gate electrode of the field effect transistor 27. Thisaction increases the drain-to-source current and in turn increases thesource voltage thereof. When the source voltage exceeds the zenervoltage of the zener diode 29, it drives the silicon controlledrectifier 30 into conduction to form a short-circuit between theconductors 1 and 2.

The frequency filtering section 18 consists of an electromechanicalfilter consisting of a tuning fork 32, an electromagnet 31 serving as amagnetostrictive conversion element magnetically coupled to one leg ofthe tuning fork and a piezoelectric conversion element 34 attached tothe other leg of the tuning fork. The electromagnet 31 has a biasingwinding wound on one leg thereof and connected between the cathode ofthe silicon controlled rectifier 30 and the second terminal 5 and adriving winding wound on the other leg and connected between the bothterminals 4 and 5 through a blocking capacitor 33. The piezoelectricelement 34 is connected to the third output terminal 6 which isconnected to the third conductor 3.

As is known in the art, in the resonance condition, theelectromechanical filter of this embodiment can be represented by anequivalent four-terminal circuit as shown in FIG. 3(1). The circuitconsists of an electrical convertor section 38 consisting of a parallelcircuit of an inductance L1 and a capacitance C1, and a mechanicalconvertor section 39 consisting of a series circuit of an inductance M1,a capacitance S1 and a resistance R which correspond respectively tomass, stiffness and mechanical resistance of the mechanical portion ofthe filter. The electromagnetic filters of the detectors -1, 10-2, 10-nof this system have their own characteristic resonance frequencies f f.f,,, respectively, which are predetermined by selecting the values ofthe above structural components. When an AC signal having frequency f,is fed to the filter 18 of the detector 10-1 through the driving windingof the electromagnet 31, for example, it passes through the filter andappears at the terminal 6 since the series resonance circuit 39 does notmaterially attenuate a signal having the same frequency as its resonancefrequency f,. When the input signal has a frequency other than fhowever, the filter does not resonate and the signal is greatlyattenuated by the filter and will not appear at the terminal 6. Thiscondition can be represented by a circuit, shown in FIG. 3(2), having anopen switch 40 in place of the series resonance circuit 39.

Referring again to FIG. 2, the receiver 11 includes a variable frequencygenerator 35 connected between the terminals 7 and 8, a rectifier 36connected between the terminals 8 and 9 and an indicator 37, such as avoltmeter, for indicating the level of output of the rectifier 36. Inaddition, a relay 12, a DC source 13, and an AC source 14, an indicationlamp 15, and a sounding device 16 are arranged similarly to those in thereceiver 11 of FIG. 1.

When the detector 10-1 is excited by smoke coming in the open ionizationchamber 20, the silicon controlled rectifier 30 is driven intoconduction as described in the above to short-circuit the both terminals7 and 8 of the receiver 1 1. Therefore, the relay 12 is energized and analarm signal is generated as described in conjunction with FIG. 1. Atthe same time, the tuning fork resonator 32 is activated by the biasingwinding of the electromagnet 31.

In this condition, if the variale frequency generator 35 is operated andits frequency is varied over a wide range, and is applied to the filterthrough the driving winding of the electromagnet 31 only the frequencyf, will pass the filter and be picked up by the piezoelectric element 34and appear at the output terminal 6. This signal is transmitted throughthe conductor 3 to the receiver 11 and rectified by the rectifier 36 andits level is indicated by the indicator 37. Therefore, the excitation ofdetector 10-1 can be determined at the receiver 11 by reading thefrequency of the variable frequency generator 35 corresponding to themaximum swing of the indicator 37. Similarly when any of the otherdetectors is excited, the excited detector can be determined by thefrequency which gives a maximum swing of the indicator 37.

FIG. 4 shows another embodiment of an ionization smoke detectorincluding a modification of the electromechanical filter shown in FIG.2. In this embodiment, the mechanical filter consists of a drivingmagnet 31, a tuning fork 32 and a pick-up magnet 41. The driving magnet31 has a leg which includes a permanent magnet for constantly biasingthe tuning fork 32 in an activated state. The AC signal applied from thevariable frequency generator 35 to the terminal 4 passes through thesilicon controlled rectifier 30 and the driving winding of the drivingmagnet 31 in superposition with the DC current applied from the powersupply 13 and is picked up by the pick-up winding of the pick-up magnet41 when the detector is excited.

Since in the above mentioned embodiments the electromechanical filter isused as a four-terminal network, the system requires at least threeconductors. However, it has been well known in the art that suchelectromechanical filters having four terminals can be changed into atwo-terminal network by terminating both output terminals with asuitable resistor. In this case, the equivalent circuit of the filtercan be represented by the circuit of FIG. 5(1) in its resonant state orby the circuit of FIG. 5(2) in its nonresonant state. As in the case ofFIG. 3, a signal having a resonant frequency of a given detector canpass through the series resonant circuit 39 but other signals havingother frequencies can pass through neither the series resonance circuit39 not the parallel resonance circuit 38 and is blocked by the filter.By applying this principle to the system, the number of necessaryconductors can be reduced on two.

Each of the detectors may be provided with a sounding device to producean audible alarm upon the excitation of a detector. This can be simplyaccomplished by attaching a dynamic speaker to one leg of the tuningfork as shown in FIG. 6(1). In the drawing, a tuning fork resonator 32has an input piezoelectric element 60 and an output piezoelectricelement 61. A permanent magnet 62 is attached to one leg 58 of thetuning fork and is surrounded by a voice coil 64 of a speaker 63. Thisarrangement is symbolized by the structure denoted by the numeral 71 inthe equivalent circuit diagram of FIG. 6(2). When the tuning fork isdriven into resonant condition, the permanent magnet 62 vibrates withthe leg 58 at its resonance frequency and induces an audio current inthe voice coil 64. Again due to interaction between the audio currentand the permanent magnet 62, the voice coil 64 vibrates at the audiofrequency and sounds the speaker 63.

Referring next to FIG. 7 representing another embodiment of the systemof this invention, a plurality of detectors -1, 10-2, 10n of which 10-1is shown in detail in a sectional view while the others are shownschematically in block form. All of the detectors are connected inparallel between a pair of conductors 1 and 2 which are respectivelyconnected to a pair of input terminals 7 and 8 of a receiver 11. Theother ends of the conductors 1 and 2 are terminated with a highpassfilter 42 which blocks the DC component of a signal but serves as aspecific impedance for the AC component thereof.

The detectors 10-1, 10-2 10-n, respectively, consist ofelectromechanical filter sections 18-1, 18-2, 18-n and normally openswitch sections 40-1, 40-2 40-n. The switch sections are connected inparallel between the pair of conductors 1 and 2 but the filter sectionsare connected in series with the first conductor 1. As hereinafterdescribed, the switch sections consist of similar normally open contactswitches operated by a bimetal element and the filter sections consistof tuning fork resonators having their own characteristic resonantfrequencies f 'f .f respectively.

As shown in detail in the dashed block of the detector 10-1, each of thedetectors comprises a cylindrical housing 51 made of a suitable materialsuch as metal or synthetic resin, an insulating base 52 fixed to thebottom of the housing 51 for supporting an insulating support rod 55 anda tuning fork 32, a thermally deformable heat sensing element 53 such asbimetal plate fixed to the top of the housing 51 and a mesh cover 54.The support rod 55 extends upwardly through the heat sensing element 53so as not to interfere with its movement and supports at its upper end apair of normally open contacts 56 and 57. The heat sensing element 53has an original shape which is concave downwardly as shown by dottedlines in the drawing and has a contact block 59 fixed to the lower facethereof, and is so arranged that the contact block 59 contacts with thetop of the tuning fork 32 to suppress its vibration in the originalstate but it is deformed thermally into a shape which is upwardly convexas shown in the drawing and the upper face of the element 53 pushes upthe lower contact 56 into contact with the upper contact 57. The tuningfork 32 is provided with a sounding device, which is similar to thatdescribed in conjunction with FIG. 6 consisting of a permanent magnet 62fixed to one leg 58 thereof, a voice coil 64 surrounding the magnet62and a speaker horn 63 attached to the voice coil 64. A hole 65 is formedin the wall of the housing 51 to emit sound generated by the speaker.The insulating base 52 is also provided with connector pins 66, 67, 68,69 and 70. When the detector is installed in the system, as shown in thedrawing, the contacts 56 and 57 areconnected respectively through theconnector pins 66 and 67 to the conductors 1 and 2 and the tuning forkresonator 32 is connected in series with the first conductor 1 throughthe piezoelectric elements 60 and 61 and the connector pins 69 and 70.

The equivalent circuit of the tuning fork resonator 32 of thisembodiment is shown in FIG. 5(1) in' the resonant state and in FIG. 5(2)in a nonresonant state.

Since it is assumed in FIG. 7 that only the detector 10-1 is excited,the switch sections of the other detectors are indicated as being openand the series resonant circuits 39' (FIG. 5) are omitted from thefilter sections of the other detectors.

The receiver 11 also includes an electromagnetic relay. 12, a powersupply 13, another power supply 14, an indicating lamp 15 and a soundingdevice 16 which serve the same functions as those of FIG. 1. Inaddition, the receiver 11 includes a low-pass filter 43 consisting of achoke coil 45 and capacitors 46 and 47 and is connected between therelay 12 and the power supply 13. A high-pass filter 14 consisting of achoke coil 40 and capacitors 49 and 50 is connected between theterminals 7 and 8. Between the high pass filter 44 and the terminal 8there are also connected a variable frequency generator 35 and anindicator 37. The indicator 37 has a plurality of indicating lamps whichcorrespond respectively to the detectors 10-1, 10-2, 10-n in the systemand can be illuminated by an AC current having a level higher than aspecific value. The indicator 37 is interlocked with the variablefrequency generator 35 so that the indicating lamps respectivelycorrespond to the detectors 10-1 to 10-n are successively switched intothe line in correspondence with the successive change of frequency fromf to f of the generator 35. The other end of the power supply 13 and theterminal 8 are grounded as shown in the drawing. Thus the DC componentof the input signal flows through the relay 12 and the AC componentflows through the indicator 37.

In operation, if a detector is not excited, all of the switch sections40-1 through 40-n are open and all of the filter sections 18-1 through18-n are in the condition as shown in FIG. 5(2). Therefore, even thoughthe frequency of the generator 35 is varied from f, to f,,, there isneither a DC current nor an AC current flowing through the conductors 1and 2 because a closed circuit is not formed for the both DC and ACsignal component. However, when one of the detectors, for example thefirst detector 10-1 as shown in FIG. 7, is excited, that is, when theheat sensing element 53 is heated to cause the bimetal to deflectupwardly as shown by full lines in the drawing, the lower contact 56 ispushed up into contact with the upper contact 57 to short-circuit theconductors 1 and 2 and at the same time, the contact block 59 leaves thetop of the tuning fork 32 to permit it to vibrate. In this condition,the DC component can flow through the relay 12 to generate an alarmsignal and the AC component of frequency f, which has been blocked onlyby'the filter section of the detector 10-1 flows in the indicator 37 toflash the corresponding lamp. Therefore, if the variable frequencygenerator 35 is continuously varied over the full range of frequency,the activated detector is automatically indicated on the indicator 37 atthe same time an alarm signal is given when any of the detectors isactivated by fire.

FIG. 8 represents a variation of the receiverll. In this receiver, thevariable frequency generator 35 of the foregoing receiver is replaced bya plurality of fixed frequency generators 35-1, 35-2, 35-3, 35-n whichgenerate frequencies f,, f f f,,, respectively, and the indicating meansconsists of a plurality of groups respectively corresponding to thefrequencies f and f and consisting of band-pass filters 74-1 to 74-nhaving characteristic pass-frequenciesf, to f, respectively, am-

plifiers 75-1 to 75-n, rectifiers 76-1 to 76-n and indicating lamps 77-1to 77-n.

In operation, AC signals having frequencies f, to f,,, respectively, aregenerated by the generators 35-1 to 35-n, amplified by an amplifier 72and applied through a chopper 73 to a parallel connection of detectors10-1 to 10-n and terminals 7 and 8. If one of the detectors is excitedand passes its characteristic frequency, tis frequency is fed back tothe receiver 11, filtered by a corresponding band-pass filter, amplifiedand rectified and flashes one of the indicating lamps which indicatesthe excited detector. It is obvious that the fire alarm device whichhandles the DC component is the same as that of the foregoingembodiments, though it is not indicated in the receiver 11 of FIG. 8.

As described in the above, according to this invention, the site of thefire can be easily determined at the receiver and this makes it possibleto centrally control a number of fire alarm systems. Moreover, thedetectors according to this invention are rather simple in constructionand can be manufactured at low cost.

It should be noted that the abovementioned embodiments of this inventionare presented only for the purpose of illustration, and variousmodifications and changes can be made without departing from the spiritand scope of the invention. For example, though the filter used in eachdetector is indicated as an electromechanical filter and especially atuning fork resonator, any other type of band-pass filter havingsuitable narrow frequency characteristics can be adopted. Moreover,though the detectors are illustrated as ionization types and bimetaltypes, any other type of detector having a normally open switchingcircuit which is closed when the detector is excited can be used as theoccasion demands.

What is claimed is:

1. A fire alarm system comprising a plurality of fire sensing unitsconnected in parallel between a pair of conductors, a receiving unitincluding a voltage source and an alarm device connected to saidconductors, each of said fire sensing units including a normally openswitch which is closed to short circuit said conductors and energizesaid alarm device when a fire is sensed, each fire sensing unit furtherincluding a band pass filter connected between said conductors andhaving a characteristic resonant frequency preselected peculiarly tosaid sensing unit, said receiving unit further including means forgenerating a range of AC signals having frequencies corresponding tosaid characteristic resonant frequencies of said filters in therespective sensing units, each of said filters being operated uponactuation of its associated sensing unit to produce its characteristicfrequency, a conductor directly connecting the outputs of said filtersin said sensing units to said receiving unit and means in said receivingunit and connected with the last said conductor for discriminating thefrequencies of the received AC signals and indicating the specificdetector activated by the presence of fire whereby each detector uponactivation produces both a general alarm and an indicating signal toidentify at the receiving unit the specific detector actuated.

2. A fire alarm system according to claim 1 wherein each of said filtersis an electromechanical band pass filter and each of said detectorsincludes a sounding device driven by said electromechanical filter.

3. A fire alarm system according to claim 1 wherein said indicatingmeans includes a plurality of electric lamps.

4. A fire alarm system according to claim 1 wherein each of said firesensing units sense both ambient temperature and smoke.

1. A fire alarm system comprising a plurality of fire sensing unitsconnected in parallel between a pair of conductors, a receiving unitincluding a voltage source and an alarm device connected to saidconductors, each of said fire sensing units including a normally openswitch which is closed to short circuit said conductors and energizesaid alarm device when a fire is sensed, each fire sensing unit furtherincluding a band pass filter connected between said conductors andhaving a characteristic resonant frequency preselected peculiarly tosaid sensing unit, said receiving unit further including means forgenerating a range of AC signals having frequencies corresponding tosaid characteristic resonant frequencies of said filters in therespective sensing units, each of said filters being operated uponactuation of its associated sensing unit to produce its characteristicfrequency, a conductor directly connecting the outputs of said filtersin said sensing units to said receiving unit and means in said receivingunit and connected with the last said conductor for discriminating thefrequencies of the received AC signals and indicating the specificdetector activated by the presence of fire whereby each detector uponactivation produces both a general alarm and an indicating signal toidentify at the receiving unit the specific detector actuated.
 2. A firealarm system according to claim 1 wherein each of said filters is anelectromechanical band pass filter and each of said detectors includes asounding device driven by said electromechanical filter.
 3. A fire alarmsystem according to claim 1 wherein said indicating means includes aplurality of electric lamps.
 4. A fire alarm system according to claim 1wherein each of said fire sensing units sense both ambient temperatureand smoke.